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systemd/man/systemd-cryptenroll.xml
Zbigniew Jędrzejewski-Szmek b66a6e1a58 man: "the initial RAM disk" → "the initrd" 
In many places we spelled out the phrase behind "initrd" in full, but this
isn't terribly useful. In fact, no "RAM disk" is used, so emphasizing this
is just confusing to the reader. Let's just say "initrd" everywhere, people
understand what this refers to, and that it's in fact an initramfs image.

Also, s/i.e./e.g./ where appropriate.

Also, don't say "in RAM", when in fact it's virtual memory, whose pages
may or may not be loaded in page frames in RAM, and we have no control over
this.

Also, add <filename></filename> and other minor cleanups.
2022-09-20 16:48:50 +02:00

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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-cryptenroll" xmlns:xi="http://www.w3.org/2001/XInclude" conditional='HAVE_LIBCRYPTSETUP'>
<refentryinfo>
<title>systemd-cryptenroll</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-cryptenroll</refentrytitle>
<manvolnum>1</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-cryptenroll</refname>
<refpurpose>Enroll PKCS#11, FIDO2, TPM2 token/devices to LUKS2 encrypted volumes</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>systemd-cryptenroll <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">DEVICE</arg></command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-cryptenroll</command> is a tool for enrolling hardware security tokens and devices
into a LUKS2 encrypted volume, which may then be used to unlock the volume during boot. Specifically, it
supports tokens and credentials of the following kind to be enrolled:</para>
<orderedlist>
<listitem><para>PKCS#11 security tokens and smartcards that may carry an RSA key pair (e.g. various
YubiKeys)</para></listitem>
<listitem><para>FIDO2 security tokens that implement the <literal>hmac-secret</literal> extension (most
FIDO2 keys, including YubiKeys)</para></listitem>
<listitem><para>TPM2 security devices</para></listitem>
<listitem><para>Regular passphrases</para></listitem>
<listitem><para>Recovery keys. These are similar to regular passphrases, however are randomly generated
on the computer and thus generally have higher entropy than user-chosen passphrases. Their character
set has been designed to ensure they are easy to type in, while having high entropy. They may also be
scanned off screen using QR codes. Recovery keys may be used for unlocking LUKS2 volumes wherever
passphrases are accepted. They are intended to be used in combination with an enrolled hardware
security token, as a recovery option when the token is lost.</para></listitem>
</orderedlist>
<para>In addition, the tool may be used to enumerate currently enrolled security tokens and wipe a subset
of them. The latter may be combined with the enrollment operation of a new security token, in order to
update or replace enrollments.</para>
<para>The tool supports only LUKS2 volumes, as it stores token meta-information in the LUKS2 JSON token
area, which is not available in other encryption formats.</para>
</refsect1>
<refsect1>
<title>Limitations</title>
<para>Note that currently when enrolling a new key of one of the five supported types listed above, it is
required to first provide a passphrase or recovery key (i.e. one of the latter two key types). For
example, it's currently not possible to unlock a device with a FIDO2 key in order to enroll a new FIDO2
key. Instead, in order to enroll a new FIDO2 key, it is necessary to provide an already enrolled regular
passphrase or recovery key. Thus, if in future key roll-over is desired it's generally recommended to
combine TPM2, FIDO2, PKCS#11 key enrollment with enrolling a regular passphrase or recovery key.</para>
<para>Also note that support for enrolling multiple FIDO2 tokens is currently not too useful, as while
unlocking <command>systemd-cryptsetup</command> cannot identify which token is currently plugged in and
thus does not know which authentication request to send to the device. This limitation does not apply to
tokens enrolled via PKCS#11 — because tokens of this type may be identified immediately, before
authentication.</para>
</refsect1>
<refsect1>
<title>Options</title>
<para>The following options are understood:</para>
<variablelist>
<varlistentry>
<term><option>--password</option></term>
<listitem><para>Enroll a regular password/passphrase. This command is mostly equivalent to
<command>cryptsetup luksAddKey</command>, however may be combined with
<option>--wipe-slot=</option> in one call, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--recovery-key</option></term>
<listitem><para>Enroll a recovery key. Recovery keys are mostly identical to passphrases, but are
computer-generated instead of being chosen by a human, and thus have a guaranteed high entropy. The
key uses a character set that is easy to type in, and may be scanned off screen via a QR code.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--unlock-key-file=</option><replaceable>PATH</replaceable></term>
<listitem><para>Use a file instead of a password/passphrase read from stdin to unlock the volume.
Expects the PATH to the file containing your key to unlock the volume. Currently there is nothing like
<option>--key-file-offset=</option> or <option>--key-file-size=</option> so this file has to only
contain the full key.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--pkcs11-token-uri=</option><replaceable>URI</replaceable></term>
<listitem><para>Enroll a PKCS#11 security token or smartcard (e.g. a YubiKey). Expects a PKCS#11
smartcard URI referring to the token. Alternatively the special value <literal>auto</literal> may
be specified, in order to automatically determine the URI of a currently plugged in security token
(of which there must be exactly one). The special value <literal>list</literal> may be used to
enumerate all suitable PKCS#11 tokens currently plugged in. The security token must contain an RSA
key pair which is used to encrypt the randomly generated key that is used to unlock the LUKS2
volume. The encrypted key is then stored in the LUKS2 JSON token header area.</para>
<para>In order to unlock a LUKS2 volume with an enrolled PKCS#11 security token, specify the
<option>pkcs11-uri=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
<programlisting>myvolume /dev/sda1 - pkcs11-uri=auto</programlisting>
<para>See
<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
<filename>/etc/crypttab</filename> line.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--fido2-credential-algorithm=</option><replaceable>STRING</replaceable></term>
<listitem><para>Specify COSE algorithm used in credential generation. The default value is
<literal>es256</literal>. Supported values are <literal>es256</literal>, <literal>rs256</literal>
and <literal>eddsa</literal>.</para>
<para><literal>es256</literal> denotes ECDSA over NIST P-256 with SHA-256. <literal>rs256</literal>
denotes 2048-bit RSA with PKCS#1.5 padding and SHA-256. <literal>eddsa</literal> denotes
EDDSA over Curve25519 with SHA-512.</para>
<para>Note that your authenticator may not support some algorithms.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--fido2-device=</option><replaceable>PATH</replaceable></term>
<listitem><para>Enroll a FIDO2 security token that implements the <literal>hmac-secret</literal>
extension (e.g. a YubiKey). Expects a <filename>hidraw</filename> device referring to the FIDO2
device (e.g. <filename>/dev/hidraw1</filename>). Alternatively the special value
<literal>auto</literal> may be specified, in order to automatically determine the device node of a
currently plugged in security token (of which there must be exactly one). The special value
<literal>list</literal> may be used to enumerate all suitable FIDO2 tokens currently plugged in. Note
that many hardware security tokens that implement FIDO2 also implement the older PKCS#11
standard. Typically FIDO2 is preferable, given it's simpler to use and more modern.</para>
<para>In order to unlock a LUKS2 volume with an enrolled FIDO2 security token, specify the
<option>fido2-device=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
<programlisting>myvolume /dev/sda1 - fido2-device=auto</programlisting>
<para>See
<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
<filename>/etc/crypttab</filename> line.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--fido2-with-client-pin=</option><replaceable>BOOL</replaceable></term>
<listitem><para>When enrolling a FIDO2 security token, controls whether to require the user to enter
a PIN when unlocking the volume (the FIDO2 <literal>clientPin</literal> feature). Defaults to
<literal>yes</literal>. (Note: this setting is without effect if the security token does not support
the <literal>clientPin</literal> feature at all, or does not allow enabling or disabling
it.)</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--fido2-with-user-presence=</option><replaceable>BOOL</replaceable></term>
<listitem><para>When enrolling a FIDO2 security token, controls whether to require the user to
verify presence (tap the token, the FIDO2 <literal>up</literal> feature) when unlocking the volume.
Defaults to <literal>yes</literal>. (Note: this setting is without effect if the security token does not support
the <literal>up</literal> feature at all, or does not allow enabling or disabling it.)
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--fido2-with-user-verification=</option><replaceable>BOOL</replaceable></term>
<listitem><para>When enrolling a FIDO2 security token, controls whether to require user verification
when unlocking the volume (the FIDO2 <literal>uv</literal> feature). Defaults to
<literal>no</literal>. (Note: this setting is without effect if the security token does not support
the <literal>uv</literal> feature at all, or does not allow enabling or disabling it.)</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--tpm2-device=</option><replaceable>PATH</replaceable></term>
<listitem><para>Enroll a TPM2 security chip. Expects a device node path referring to the TPM2 chip
(e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal> may
be specified, in order to automatically determine the device node of a currently discovered TPM2
device (of which there must be exactly one). The special value <literal>list</literal> may be used to
enumerate all suitable TPM2 devices currently discovered.</para>
<para>In order to unlock a LUKS2 volume with an enrolled TPM2 security chip, specify the
<option>tpm2-device=</option> option in the respective <filename>/etc/crypttab</filename> line:</para>
<programlisting>myvolume /dev/sda1 - tpm2-device=auto</programlisting>
<para>See
<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
more comprehensive example of a <command>systemd-cryptenroll</command> invocation and its matching
<filename>/etc/crypttab</filename> line.</para>
<para>Use <option>--tpm2-pcrs=</option> (see below) to configure which TPM2 PCR indexes to bind the
enrollment to.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--tpm2-pcrs=</option><arg rep="repeat">PCR</arg></term>
<listitem><para>Configures the TPM2 PCRs (Platform Configuration Registers) to bind the enrollment
requested via <option>--tpm2-device=</option> to. Takes a <literal>+</literal> separated list of
numeric PCR indexes in the range 0…23. If not used, defaults to PCR 7 only. If an empty string is
specified, binds the enrollment to no PCRs at all. PCRs allow binding the enrollment to specific
software versions and system state, so that the enrolled unlocking key is only accessible (may be
"unsealed") if specific trusted software and/or configuration is used.</para>
<table>
<title>Well-known PCR Definitions</title>
<!-- See: https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/ -->
<!-- See: https://github.com/rhboot/shim/blob/main/README.tpm -->
<!-- See: https://www.gnu.org/software/grub/manual/grub/html_node/Measured-Boot.html -->
<!-- See: https://sourceforge.net/p/linux-ima/wiki/Home/ -->
<!-- See: https://github.com/tianocore-docs/edk2-TrustedBootChain/blob/main/4_Other_Trusted_Boot_Chains.md -->
<!-- See: https://wiki.archlinux.org/title/Trusted_Platform_Module#Accessing_PCR_registers -->
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="pcr" />
<colspec colname="definition" />
<thead>
<row>
<entry>PCR</entry>
<entry>Explanation</entry>
</row>
</thead>
<tbody>
<row>
<entry>0</entry>
<entry>Core system firmware executable code; changes on firmware updates</entry>
</row>
<row>
<entry>1</entry>
<entry>Core system firmware data/host platform configuration; typically contains serial and model numbers, changes on basic hardware/CPU/RAM replacements</entry>
</row>
<row>
<entry>2</entry>
<entry>Extended or pluggable executable code; includes option ROMs on pluggable hardware</entry>
</row>
<row>
<entry>3</entry>
<entry>Extended or pluggable firmware data; includes information about pluggable hardware</entry>
</row>
<row>
<entry>4</entry>
<entry>Boot loader and additional drivers; changes on boot loader updates. The shim project will measure the PE binary it chain loads into this PCR. If the Linux kernel is invoked as UEFI PE binary, it is measured here, too. <citerefentry><refentrytitle>sd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures system extension images read from the ESP here too (see <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>).</entry>
</row>
<row>
<entry>5</entry>
<entry>GPT/Partition table; changes when the partitions are added, modified or removed</entry>
</row>
<row>
<entry>6</entry>
<entry>Power state events; changes on system suspend/sleep</entry>
</row>
<row>
<entry>7</entry>
<entry>Secure boot state; changes when UEFI SecureBoot mode is enabled/disabled, or firmware certificates (PK, KEK, db, dbx, …) changes. The shim project will measure most of its (non-MOK) certificates and SBAT data into this PCR.</entry>
</row>
<!-- Grub measures all its commands and the kernel command line into PCR 8… -->
<!-- Grub measures all files it reads (including kernel image, initrd, …) into PCR 9… -->
<row>
<entry>9</entry>
<entry>The Linux kernel measures all initrds it receives into this PCR.</entry>
<!-- Strictly speaking only Linux >= 5.17 using the LOAD_FILE2 protocol, see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f046fff8bc4c4d8f8a478022e76e40b818f692df -->
</row>
<row>
<entry>10</entry>
<entry>The IMA project measures its runtime state into this PCR.</entry>
</row>
<row>
<entry>11</entry>
<entry><citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures the ELF kernel image, embedded initrd and other payload of the PE image it is placed in into this PCR. Unlike PCR 4 (where the same data should be measured into), this PCR value should be easy to pre-calculate, as this only contains static parts of the PE binary. Use this PCR to bind TPM policies to a specific kernel image, possibly with an embedded initrd.</entry>
</row>
<row>
<entry>12</entry>
<entry><citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures any specified kernel command line into this PCR. <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures any manually specified kernel command line (i.e. a kernel command line that overrides the one embedded in the unified PE image) and loaded credentials into this PCR. (Note that if <command>systemd-boot</command> and <command>systemd-stub</command> are used in combination the command line might be measured twice!)</entry>
</row>
<row>
<entry>13</entry>
<entry><citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures any <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry> images it loads and passed to the booted kernel into this PCR.</entry>
</row>
<row>
<entry>14</entry>
<entry>The shim project measures its "MOK" certificates and hashes into this PCR.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>For most applications it should be sufficient to bind against PCR 7 (and possibly PCR 14, if
shim/MOK is desired), as this includes measurements of the trusted certificates (and possibly hashes)
that are used to validate all components of the boot process up to and including the OS kernel. In
order to simplify firmware and OS version updates it's typically not advisable to include PCRs such
as 0 and 2 in the binding of the enrollment, since the program code they cover should already be
protected indirectly through the certificates measured into PCR 7. Validation through these
certificates is typically preferable over validation through direct measurements as it is less
brittle in context of OS/firmware updates: the measurements will change on every update, but code
signatures likely will validate against pre-existing certificates.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--tpm2-with-pin=</option><replaceable>BOOL</replaceable></term>
<listitem><para>When enrolling a TPM2 device, controls whether to require the user to enter a PIN
when unlocking the volume in addition to PCR binding, based on TPM2 policy authentication. Defaults
to <literal>no</literal>. Despite being called PIN, any character can be used, not just numbers.
</para>
<para>Note that incorrect PIN entry when unlocking increments the TPM dictionary attack lockout
mechanism, and may lock out users for a prolonged time, depending on its configuration. The lockout
mechanism is a global property of the TPM, <command>systemd-cryptenroll</command> does not control or
configure the lockout mechanism. You may use tpm2-tss tools to inspect or configure the dictionary
attack lockout, with <citerefentry
project='mankier'><refentrytitle>tpm2_getcap</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and <citerefentry
project='mankier'><refentrytitle>tpm2_dictionarylockout</refentrytitle><manvolnum>1</manvolnum></citerefentry>
commands, respectively.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--tpm2-public-key=</option><arg>PATH</arg></term>
<term><option>--tpm2-public-key-pcrs=</option><arg rep="repeat">PCR</arg></term>
<term><option>--tpm2-signature=</option><arg>PATH</arg></term>
<listitem><para>Configures a TPM2 signed PCR policy to bind encryption to. The
<option>--tpm2-public-key=</option> option accepts a path to a PEM encoded RSA public key, to bind
the encryption to. If this is not specified explicitly, but a file
<filename>tpm2-pcr-public-key.pem</filename> exists in one of the directories
<filename>/etc/systemd/</filename>, <filename>/run/systemd/</filename>,
<filename>/usr/lib/systemd/</filename> (searched in this order), it is automatically used. The
<option>--tpm2-public-key-pcrs=</option> option takes a list of TPM2 PCR indexes to bind to (same
syntax as <option>--tpm2-pcrs=</option> described above). If not specified defaults to 11 (i.e. this
binds the policy to any unified kernel image for which a PCR signature can be provided).</para>
<para>Note the difference between <option>--tpm2-pcrs=</option> and
<option>--tpm2-public-key-pcrs=</option>: the former binds decryption to the current, specific PCR
values; the latter binds decryption to any set of PCR values for which a signature by the specified
public key can be provided. The latter is hence more useful in scenarios where software updates shell
be possible without losing access to all previously encrypted LUKS2 volumes.</para>
<para>The <option>--tpm2-signature=</option> option takes a path to a TPM2 PCR signature file
as generated by the
<citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool. If this this is not specified explicitly a suitable signature file
<filename>tpm2-pcr-signature.json</filename> is searched for in <filename>/etc/systemd/</filename>,
<filename>/run/systemd/</filename>, <filename>/usr/lib/systemd/</filename> (in this order) and
used. If a signature file is specified or found it is used to verify if the volume can be unlocked
with it given the current PCR state, before the new slot is written to disk. This is intended as
safety net to ensure that access to a volume is not lost if a public key is enrolled for which no
valid signature for the current PCR state is available. If the supplied signature does not unlock the
current PCR state and public key combination, no slot is enrolled and the operation will fail. If no
signature file is specified or found no such safety verification is done.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--wipe-slot=</option><arg rep="repeat">SLOT</arg></term>
<listitem><para>Wipes one or more LUKS2 key slots. Takes a comma separated list of numeric slot
indexes, or the special strings <literal>all</literal> (for wiping all key slots),
<literal>empty</literal> (for wiping all key slots that are unlocked by an empty passphrase),
<literal>password</literal> (for wiping all key slots that are unlocked by a traditional passphrase),
<literal>recovery</literal> (for wiping all key slots that are unlocked by a recovery key),
<literal>pkcs11</literal> (for wiping all key slots that are unlocked by a PKCS#11 token),
<literal>fido2</literal> (for wiping all key slots that are unlocked by a FIDO2 token),
<literal>tpm2</literal> (for wiping all key slots that are unlocked by a TPM2 chip), or any
combination of these strings or numeric indexes, in which case all slots matching either are
wiped. As safety precaution an operation that wipes all slots without exception (so that the volume
cannot be unlocked at all anymore, unless the volume key is known) is refused.</para>
<para>This switch may be used alone, in which case only the requested wipe operation is executed. It
may also be used in combination with any of the enrollment options listed above, in which case the
enrollment is completed first, and only when successful the wipe operation executed — and the newly
added slot is always excluded from the wiping. Combining enrollment and slot wiping may thus be used to
update existing enrollments:</para>
<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=tpm2 --tpm2-device=auto</programlisting>
<para>The above command will enroll the TPM2 chip, and then wipe all previously created TPM2
enrollments on the LUKS2 volume, leaving only the newly created one. Combining wiping and enrollment
may also be used to replace enrollments of different types, for example for changing from a PKCS#11
enrollment to a FIDO2 one:</para>
<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=pkcs11 --fido2-device=auto</programlisting>
<para>Or for replacing an enrolled empty password by TPM2:</para>
<programlisting>systemd-cryptenroll /dev/sda1 --wipe-slot=empty --tpm2-device=auto</programlisting>
</listitem>
</varlistentry>
<xi:include href="standard-options.xml" xpointer="help" />
<xi:include href="standard-options.xml" xpointer="version" />
</variablelist>
</refsect1>
<refsect1>
<title>Exit status</title>
<para>On success, 0 is returned, a non-zero failure code otherwise.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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